The Force can be with groups and individuals who haven’t trained before. Luke and Leia had been with the Ewoks, and their thoughts might have been a catalyst for the Force to be in their presence. Also, the Endor fight concerned the Force on both sides, so there could have been a heavy Force presence in general.
I don’t remember anything in the films supporting this theory.
I guess you must have never watched a Star Wars film before, then.
It’s seriously the basis of the force, that it is present in all things, moving and guiding everything. Leia has it, without training. And in TFA, which you seem to be a fan of, Rey is strong with the force despite no training, stronger even than Kylo. And she employs it without even knowing she can.
And it’s the basis of characters saying “May the force be with you”, even non trained characters to other non trained characters.